Fluorosurfactants are typically used as a polymerization aid in the dispersion polymerization of fluoropolymers, the fluorosurfactants functioning as a non-telogenic dispersing agent. For example, an early description of this use of fluorosurfactants is found in U.S. Pat. No. 2,559,752 (Berry). Because of environmental concerns and because fluorosurfactants are expensive, processes have been developed for their recovery from waste water and from aqueous fluoropolymer dispersions.
One method for removal of fluorosurfactants from fluoropolymer dispersions is disclosed in U.S. Pat. No. 4,369,266 and includes the addition of a stabilizing surfactant followed by concentration by ultrafiltration. This patent teaches that a high proportion of the fluorosurfactant can be removed via the aqueous permeate. It is also known to remove fluorosurfactant by adsorption onto an ion exchange resin as taught in U.S. Pat. No. 3,882,153 (Seki et al) and U.S. Pat. No. 4,282,162 (Kuhls). Kuhls teaches recovery of fluorinated emulsifiers dissolved in the aqueous phase after coagulation of the polymer from the dispersion or in aqueous polymer dispersions to be concentrated. US 2003/0125421 A1 (Bladel et al.) also teaches removal of fluorine-containing emulsifiers from fluoropolymer dispersion by contacting with an anion exchanger.
Known processes using anion exchange resins for the removal of fluorosurfactant from fluoropolymer dispersions employ either strongly basic anion exchange resins or weakly basic anion exchange resins. However, the resins employed have had a broad Gaussian or conventional distribution of bead sizes about the average bead diameter. Thus, conventional resin beads range in size from 16 to 50 mesh, or 1200 to 300 microns. For example, Bladel et al. teaches to the use of a resin sold by Rohm and Haas under the trademark AMBERLITE® 402 which is known to have the a conventional 16-50 mesh particle size particle distribution for anion exchange resins of this type.
Anion exchange resin beads with the conventional bead size distribution typically have very large beads which become increasingly fragile as they get larger and are prone to breakage. Breakage can result in fine particles which may contaminate the dispersion being treated and/or produce larger broken particles with jagged edges. When a fixed anion exchange bed is employed, anion exchange beads with the conventional bead size distribution and/or with broken particles with jagged edges are susceptible to tight particle packing resulting in nonuniform, tortuous channels in the bed. This can result in high shear conditions in the bed, increasing the risk of coagulation of the dispersion. With conventional anion exchange resins in fixed beds, long treatment times are therefore required and care much be taken to prevent coagulation, especially with high solids content dispersions, i.e., greater then 25% solids.